dup.c

#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>

int main() {
	printf("before\n");

	int dupfd = dup(STDOUT_FILENO);
	if (dupfd < 0) {
		return 1;
	}
	int newfd = open("/tmp/out", O_RDWR | O_CREAT | O_TRUNC);
	if (newfd < 0) {
		return 2;
	}
	if (dup2(newfd, STDOUT_FILENO) < 0) {
		return 3;
	}
	if (close(newfd) != 0) {
		return 4;
	}

	printf("hello\n");

	if (dup2(dupfd, STDOUT_FILENO) < 0) {
		return 5;
	}
	close(dupfd);

	printf("after\n");
}